An arch wire is the wire that
attaches to your braces. It is called an "arch wire" because
your top teeth comprise your top arch, and your bottom teeth
comprise your bottom arch. An arch wire is like the engine
that guides and moves your teeth. Without an arch wire to
connect your braces, you would just be wearing braces for
fun and your teeth would never move! Arch wires come in
different sizes and have different material compositions.
Strength and Springiness
When you first start
treatment with braces, your teeth are crooked. The wire that
attaches to your braces must be able to return to its
original shape when it is deformed or bent. The force that
returns the wire to its original shape is what moves your
teeth. The wire should be springy, yet exert a gentle force
so that your brackets do not pop off when the orthodontist
ties in your arch wire.
As your teeth get
straighter, your orthodontist will exchange your wires for
stronger wires that are usually less elastic and stiffer.
These stronger, stiffer wires allow the orthodontist to have
more control over tooth movements. Often times, these later
wires have characteristics that allow the orthodontist to
put permanent bends in the arch wire if he wants to move
Size of Arch Wires
When orthodontists talk
about the “size” of an arch wire, they are referring to the
cross-section or thickness of the wire. Considering arch
wires made from identical materials, the smaller the
cross-section, the more elastic and less stiff the wire will
be. Wires come in two types of cross-sections: 1) Round and
2) Rectangular. Round wires are obviously round in
cross-section. Rectangular wires can be square or
rectangular in cross section.
In the beginning stages of
treatment, round wires are typically used to level and align
the teeth. This is because when considering arch wires made
from identical materials, round wires are more elastic and
so the orthodontist will be able to engage all your teeth
into the wire without popping off brackets. If he uses a
wire that is too stiff and tries to tie the arch wire to a
really crooked tooth, the wire will put too much pressure on
the bracket, and the bracket may break off from the tooth.
After the teeth are
straighter, orthodontists usually advance to rectangular
wires. Because the wire slot of the bracket is rectangular,
a rectangular wire fits into the bracket like a hand fits
into a glove. In the beginning, the smaller rectangular wire
may be like a small hand in a large glove. However, by the
end of treatment, the rectangular wire you have may be more
like a large hand in a large glove. By fitting snugly into
the bracket, the rectangular wire controls tooth movement
better than a round wire.
Arch Wire Materials
Now that you understand a
little about why orthodontists like elastic wires in the
beginning of braces treatment and stronger, stiffer wires at
the end of treatment, let us consider what materials the
arch wires are made of.
There are three main types
of material compositions for arch wires: 1) Stainless Steel;
2) Nickel-Titanium (Ni-Ti); and 3) Beta-Titanium.
Stainless steel wires
have been used for decades due to their high strength. In
addition, stainless steel wires do not rust and can be
adjusted many different ways by the orthodontist without
breaking. However, stainless steel wires are not very
elastic, meaning that if you bend these wires too much, they
will assume the new position and will not return to their
original position. In the beginning stages of treatment, it
is important for the wires to be elastic so that the wires
can bounce back to a nice smooth U-shape and carry the teeth
with it at the same time. So as you can see, in the initial
stages of aligning very crooked teeth, stainless steel wires
may not be the best option.
wires are elastic and can return to their original shape
when deformed. Therefore, in the beginning stages of
orthodontic treatment, Ni-Ti wires are frequently used to
put gentle forces on the crooked teeth to align them. A
variation of Ni-Ti wires are heat-activated Ni-Ti (Copper
Ni-Ti) wires. Heat-activated Ni-Ti wires can hold the
deformed configuration at room temperate, but when the wire
reaches the temperature of a patient’s mouth, the wire will
return to its original shape. Heat-activated Ni-Ti wires are
useful in the beginning stages of treatment. If the teeth
are extremely crooked, the wire can be cooled so it can be
tied into the brackets easier. Then after a few minutes, it
will reach the temperature of the patient’s mouth,
displaying its Ni-Ti elastic properties. The warm wire will
want to assume its original U-shape and carry the teeth to
their new, straighter positions.
were developed after Ni-Ti wires and offer an intermediate
range of elasticity and strength, while also being able to
be permanently deformed. This wire serves as a good
intermediary wire between Ni-Ti and stainless steel. Some
orthodontists will use this wire starting in the middle of
treatment while other orthodontists do not use this type of
wire at all.
Which Wire to Use?
So which wires will your
orthodontist use? It is difficult to say because all
patients are different and all orthodontists have their own
technique for adjusting braces. Some orthodontists only use
Ni-Ti wires while other orthodontists only use stainless
steel wires. However, most orthodontists typically start
with small Ni-Ti wires to align crooked teeth in the
beginning, and progress to larger Stainless Steel or
Beta-Titanium wires when more control of teeth is necessary.
Many patients think that
their wires need to be changed at every visit. This is
usually not true. With the wide assortment of wires these
days, your orthodontist may only need to use three to five
sets of wires during treatment. More wires may be needed for
Yang, DMD, MS, is a writer and Senior Editor for
Dr. Yang received his Bachelors degree in Psychology at the
University of California at Los Angeles. Following his
undergraduate studies, Dr. Yang attended the Harvard School
of Dental Medicine, where he completed his
Evidence-Based-Dentistry thesis and obtained his Doctor of
Dental Medicine degree. After receiving his doctorate, Dr.
Yang went on to study at the University of Southern
California where he received his Certification in
Orthodontics. Concurrently at USC, he completed his thesis
on one phase versus two phase treatment in patients with
large overbites, and obtained his Masters of Science in
Dr. Yang is a Board
Certified Orthodontist, practicing in Antioch, California.
He is a Certified Invisalign Provider, and is a member of
the American Association of Orthodontists, Pacific Coast
Society of Orthodontists, American Dental Association, and
California Dental Association.